Hydrogen generator having reactant pellet with concentration gradient

ABSTRACT

A hydrogen generator is provided for generating hydrogen gas for a fuel cell stack. The hydrogen generator includes a container, and a liquid reactant storage area configured to contain a liquid including a first reactant. The hydrogen generator also includes a reaction area within the container, and a solid containing a second reactant within the reaction area and having a concentration gradient that varies along an axis such as length of the solid. The hydrogen generator further includes a liquid delivery member for delivering the liquid to the solid in the reaction area to generate hydrogen. The concentration gradient controls a reaction rate of the first and second reactants.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/593,568, filed on Aug. 24, 2012, is now U.S. Pat. No. 9,051,183; thecontents of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to a hydrogen generator,particularly a hydrogen generator for a fuel cell system, and a reactantpellet configured to efficiently react with a liquid reactant.

BACKGROUND OF THE INVENTION

Interest in fuel cell batteries as power sources for portable electronicdevices has grown. A fuel cell is an electrochemical cell that usesmaterials from outside the cell as the active materials for the positiveand negative electrode. Because a fuel cell does not have to contain allof the active materials used to generate electricity, the fuel cell canbe made with a small volume relative to the amount of electrical energyproduced compared to other types of batteries.

Fuel cells can be categorized according to the types of materials usedin the positive electrode (cathode) and negative electrode (anode)reactions. One category of fuel cell is a hydrogen fuel cell usinghydrogen as the negative electrode active material and oxygen as thepositive electrode active material. When such a fuel cell is discharged,hydrogen is oxidized at the negative electrode to produce hydrogen ionsand electrons. The hydrogen ions pass through an electricallynonconductive, ion permeable separator and the electrons pass through anexternal circuit to the positive electrode, where oxygen is reduced.

In some types of hydrogen fuel cells, hydrogen is formed from a fuelsupplied to the positive electrode side of the fuel cell, and hydrogenis produced from the supplied fuel. In other types of hydrogen fuelcells, hydrogen gas is supplied to the fuel cell from a source outsidethe fuel cell. A fuel cell system can include a fuel cell battery,including one or more fuel cells, and a hydrogen source, such as ahydrogen tank or a hydrogen generator. In some fuel cell systems, thehydrogen source can be replaced after the hydrogen is depleted.Replaceable hydrogen sources can be rechargeable or disposable.

A hydrogen generator uses one or more reactants containing hydrogen thatcan react to produce hydrogen gas. The reaction can be initiated invarious ways, such as hydrolysis and thermolysis. For example, tworeactants can produce hydrogen and byproducts when mixed together. Acatalyst can be used to catalyze the reaction. When the reactants react,reaction products including hydrogen gas and byproducts are produced.

For a hydrolysis reaction, the hydrogen generator typically employs aliquid containing a first reactant that mixes with a second solidreactant within a reaction area in a container. A liquid delivery nozzleor dispersing member is typically employed to transport the liquid froma storage area to the reaction area. The liquid delivery nozzle caninclude a tube having one or more openings through which a liquid passesinto the reaction area to mix with the second solid reactant. Thereaction causes the generation of hydrogen gas, which exits the hydrogengenerator and may be provided as fuel to a fuel cell battery.

It is desirable to provide an effective and efficient utilization of thesolid reactant upon reaction with the liquid reactant.

SUMMARY OF THE INVENTION

The above advantages are provided by a hydrogen generator and solidreactant having a concentration gradient for use in a hydrogen generatoraccording to the present invention.

A first aspect of the present invention is a hydrogen generator. Thehydrogen generating includes a container and a liquid reactant storagearea configured to contain a liquid including a first reactant. Thehydrogen generator also includes a reaction area within the container.The hydrogen generator further includes a solid containing a secondreactant within the reaction area and includes a concentration gradientthat varies along an axis of the solid. The concentration gradientcontrols a reaction rate of the first and second reactants. A liquiddelivery member delivers the liquid to the solid in the reaction area togenerate hydrogen.

Embodiments of the first aspect of the invention can include one or moreof the following features:

-   the solid includes an acid having an acid concentration that varies    along the axis of the solid to provide the concentration gradient;-   the solid includes a catalyst, wherein the catalyst varies along the    axis of the solid to provide the concentration gradient;-   the solid includes a hydrophilic material that varies along the axis    of the solid to provide the concentration gradient;-   the solid has at least one of density or porosity that varies along    the axis of the solid to provide the concentration gradient;-   the liquid delivery member includes a liquid distribution portion    having a plurality of liquid outlets;-   the liquid distribution portion has first and second ends, and a    liquid flow outlet greater at the first end than the second end,    wherein the concentration gradient has a reactant concentration that    is lowest at the first end and higher at the second end;-   the solid includes a first portion having a first reactant    concentration and a second portion having a second reactant    concentration, and the first reactant concentration is different    than the second reactant concentration;-   the first portion is closer to an inlet of the liquid delivery    member and the second portion is closer to a distal outlet of the    liquid delivery member;-   the solid further includes a third portion having a third reactant    concentration and a fourth portion having a fourth reactant    concentration;-   the axis is along a length of the solid;-   the solid is a solid body including one or more pellets;-   the second reactant includes sodium borohydride and the first    reactant includes water;-   the liquid reactant storage area is contained within the container;    and-   the hydrogen generator includes a hydrogen outlet for outputting the    generated hydrogen.

A second aspect of the present invention is a solid including a solidreactant for use in a hydrogen generator. The solid includes a firstportion extending along a first segment of a dimension of the solid andhaving a first solid reactant concentration. The solid further includesa second portion extending along a second segment of the dimension ofthe solid and having a second solid reactant concentration. The firstand second solid reactant concentrations provide a concentrationgradient along an axis of the solid.

Embodiments of the second aspect of the invention can include one ormore of the following features:

-   the solid includes an acid, wherein an acid concentration in the    first and second portions varies to provide the concentration    gradient;-   the solid includes a catalyst, wherein the catalyst in the first and    second portions varies to provide the concentration gradient;-   the solid includes a hydrophilic material that varies in the first    and second portions to provide the concentration gradient;-   the solid has at least one of density or porosity that varies in the    first and second portions to provide the concentration gradient;-   the solid includes a third portion extending along a third dimension    and having a third solid reactant concentration, wherein the third    solid reactant concentration is different than the first and second    solid reactant concentrations;-   the solid includes a fourth portion extending along a fourth    dimension and having a fourth solid reactant concentration, wherein    the fourth solid reactant concentration is different from the first,    second and third solid reactant concentrations;-   the dimension is a length;-   the solid is a solid body including one or more pellets; and-   the solid reactant includes sodium borohydride.

A further aspect of the invention is a method of generating gas with ahydrogen generator using solid body having a solid reactantconcentration gradient. The method includes forming a solid bodycontaining a solid reactant and having a solid reactant concentrationgradient that varies along an axis of the solid reactant. The methodalso includes delivering a liquid reactant to the solid reactant with aliquid delivery member to generate hydrogen, wherein the solid reactantconcentration gradient controls a reaction rate of the solid and liquidreactants. The method further includes outputting the hydrogen gas.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

Unless otherwise specified, the following definitions and methods areused herein:

-   “effluent” means non-gaseous reaction products and unreacted    reactants, solvents and additives;-   “expand” when used in describing a filter means for the filter    material to simultaneously increase in volume, increase in porosity    and decrease in density and pertains only to the material of which    the filter is made;-   “initial” means the condition of a hydrogen generator in an unused    or fresh (e.g., refilled) state, before initiating a reaction to    generate hydrogen;-   “volume exchanging relationship” means a relationship between two or    more areas or containers within a hydrogen generator such that a    quantity of volume lost by one or more of the areas or containers is    simultaneously gained by one or more of the other areas or    containers; the volume thus exchanged is not necessarily the same    physical space, so volume lost in one place can be gained in another    place;-   “concentration gradient” means a change in the concentration of a    substance from one region of a solid to another region of the solid    along an axis of the solid; and-   “reactant concentration” means the concentration of a reactant or    substance that affects the rate of reaction of the solid reactant.

Unless otherwise specified herein, all disclosed characteristics andranges are as determined at room temperature (20-25° C.).

These and other advantages of the invention will be further understoodand appreciated by those skilled in the art by reference to thefollowing written specification, claims, and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic diagram of a fuel cell system including a hydrogengenerator, according to one embodiment;

FIG. 2 is a cross-sectional view of the hydrogen generator employingsolid and liquid reactants, according to a first embodiment;

FIG. 3 is a perspective view of an unconsumed solid reactant pellethaving a concentration gradient and a liquid delivery member employed inthe hydrogen generator;

FIG. 4 is a perspective view of the solid reactant pellet partiallyconsumed and the liquid delivery member on top thereof; and

FIG. 5 is a flow diagram illustrating a process of generating hydrogengas with the hydrogen generator employing a solid reactant having aconcentration gradient, according to one embodiment.

DETAILED DESCRIPTION

The present invention includes a separate hydrogen gas generator thatcan be incorporated into a fuel cell system including a fuel cellbattery, but it is not part of the fuel cell itself. It is typically aremovable, replaceable or refillable unit that can supply hydrogen to afuel cell, rather than supplying a liquid or other fluid that isreformed by or within the fuel cell to produce hydrogen gas or protons.

The fuel cell with which the hydrogen generator can be used can be abattery containing a single fuel cell, or it can be a battery containinga plurality of fuel cells (sometimes referred to as a fuel cell stack).The fuel cell can be any type of fuel cell that uses hydrogen as a fuel.Examples include proton exchange membrane fuel cells, alkaline fuelcells and solid oxide fuel cells.

In one embodiment, a hydrogen generator includes a container with one ormore reactant storage areas, a reaction area and an effluent storagearea within the container. One or more reactant-containing liquids, eachcontaining one or more reactants, are transferred from the reactantstorage area or areas to the reaction area, where the reactant orreactants react to produce hydrogen gas and byproducts. One or morereactants can also be initially contained within the reaction area. Thereaction can be catalyzed by a catalyst, which can be initially in thereaction area or contained in a fluid transferred to the reaction area.The byproducts can include gaseous, liquid and solid reaction products.The production of hydrogen gas can force effluent from the reactionarea, through an effluent passage, to the effluent storage area. Theeffluent can include reaction byproducts as well as unreacted reactantsand additives.

The reactant-containing liquid includes a first reactant, which can bethe liquid (e.g., water), or the reactant can be mixed, suspended,dissolved or otherwise contained in the liquid. After the liquid istransported from the reactant storage area to the reaction area, itreacts with a second reactant to produce hydrogen gas. In oneembodiment, one reactant is contained in the reaction area, preferablyin a solid form as one or more pellets, and the reactant-containingliquid is transported from the reactant storage area to the reactionarea, where the reactants react to produce hydrogen gas; the reactionmay be catalyzed by a catalyst in the reaction area.

The reactant storage, reaction, and effluent storage areas may bearranged in a volume exchanging configuration such that, as reactantsare consumed during operation of the hydrogen generator, the effluentstorage area simultaneously increases in volume by moving into spacemade available by a reduction in volume of the areas initiallycontaining reactant to accommodate the effluent within the effluentstorage area. In this way the total volume of the hydrogen generator canbe minimized, since the amount of initial void volume within thehydrogen generator can be kept at a minimum (though some initial voidvolume may be necessary, if the solid and liquid reaction products havea greater volume than the initial total volume of the reactants forexample). Any suitable volume exchanging configuration can be used. Forexample, one or more areas containing reactant (e.g., a reactant storagearea and/or a reaction area containing a reactant) can be adjacent tothe effluent storage area, or the effluent storage area can be separatedfrom the areas containing reactant by one or more other components ofthe hydrogen generator that can move or otherwise allow the volumeexchange.

Hydrogen gas is separated from the liquid and solid effluent and isreleased through a hydrogen outlet to an apparatus such as a fuel cellas needed. A filter and a hydrogen permeable, liquid impermeablecomponent can be used to separate the hydrogen. The filter removessolids and may remove liquids as well, and the hydrogen permeable,liquid impermeable component removes liquids and any remaining solids,allowing only gas to pass through the hydrogen outlet. Optionally, othercomponents may be included within or downstream from the hydrogengenerator to remove other gases and impurities from the hydrogen flow.

Any or all of the reactant storage area(s), the reaction area, and theeffluent storage area can be defined by one or more of the internalsurfaces of the container and other components of the hydrogengenerator, or one or more of these areas can be enclosed by anenclosure, such as a reactant storage enclosure, a reaction areaenclosure or an effluent storage area enclosure. Such enclosures areable to undergo a change in shape (e.g., by being flexible) so theirinternal volume can decrease or increase as material exits or enters theenclosure. An enclosure can include a structure such as a bag, a balloonor a bellows, for example. The walls of an enclosure can be pleated ormade from an elastomeric material that can stretch or contract, forexample, to enable a change in internal volume. In one embodiment, anenclosure can have a wall or a portion of a wall that can stretch toprovide a larger internal volume and can apply a force to the contentsto facilitate emptying the contents.

In one embodiment, the effluent storage area is enclosed by anenclosure. One or more filter components can be fastened to theenclosure in one or more places to minimize the amount of effluent thatcan flow around the filter component. The enclosure can be or caninclude a hydrogen permeable, liquid impermeable material to separatehydrogen gas from liquids in the effluent storage area.

A liquid including a reactant can be transported from the reactantstorage area by any suitable means. For example, the liquid can bewicked, pumped, expelled by applying a force on the liquid, or acombination thereof. If the liquid is pumped, the pump can be within oroutside the hydrogen generator. The pump can be powered by a fuel cell,a battery within the hydrogen generator, or an external power source. Aforce can be applied directly against a reactant storage area enclosure,against a moveable partition in contact with either enclosure, oragainst one or more other components that make contact with or are apart of the enclosure (such as a valve assembly) for example. Force canbe provided in various ways, such as with a spring, an elastic reactantstorage enclosure that is initially stretched when full, wrapping thereactant storage enclosure with an elastic member, air or gas pressureon or within the reactant storage enclosure, the expansion of the filterin the effluent storage area, or a combination thereof.

The hydrogen generator includes a liquid delivery member that extendsinto the reaction area and is configured to deliver the liquid from thefirst reactant storage area to the reaction area. The liquid deliverymember includes a liquid distribution portion through which the liquidincluding the first reactant can pass. In various embodiments the liquiddistribution portion can include holes or slits through which the liquidcan exit, or it can be made from a material through which the liquid canpermeate or wick. These properties limit the selection of types ofmaterials that can be used. In one embodiment, the liquid distributionportion can include a tube with holes or slits which form openingstherein through which the liquid can exit. In another embodiment theliquid distribution portion can include a porous material through whichthe liquid can permeate. In another embodiment the liquid distributionportion can include a material through which the liquid can wick. In yetanother embodiment a sleeve of wicking material is provided around theliquid distribution member. This can keep solid reaction byproducts fromforming on the liquid distribution member and clogging the holes, slits,pores, etc., and preventing the flow of liquid.

The liquid delivery member may be integrally assembled to an exhaustnozzle which has an opening for allowing hydrogen gas and effluentbyproduct to exit the reaction area. The liquid delivery member mayinclude a tube that extends through or is otherwise assembled to theexhaust nozzle. The tube may be cylindrical or somewhat flattened or anyother feasible shape. The liquid delivery member may include a liquiddistribution portion made of plastic material or non-wettable fibersthat are liquid impermeable. The liquid exits the liquid distributionportion at each of the plurality of openings. A wicking member such as asponge like material may further be provided in fluid communication withthe openings to wick the liquid to the underlying solid reactant. Thegeneral shape of the delivery member may be linear, bent or any desiredshaped suitable to apply sufficient liquid to the adjacent solid. Theliquid delivery member may be assembled separate from the exhaust nozzleaccording to another embodiment.

The liquid delivery member may be configured in various shapes and sizesto achieve a desired liquid-to-solid reactant contact time and area. Theliquid-to-solid reactant contact surface may be increased by increasingthe overall length or the width of the liquid distribution member. Thelength may be increased by using a non-linear tube such as a wrap arounddesign or shaping the tube with undulations or multiple tubes.

The hydrogen generator includes a solid (e.g., a solid body or a solidmass including powders, granules, etc.) having a second reactant (solidreactant) within the reaction zone. As used below, “pellet” refers to amass of any suitable shape or size into which a solid reactant and othersolid ingredients are formed. The solid has a concentration gradientthat varies along an axis of the pellet. The axis may be a dimensionsuch as length of the solid such that the concentration gradient variesalong the length of the solid according to the embodiment shown in FIGS.3 and 4. In other embodiments, the axis may be along another dimensionsuch as width or height of the pellet or another direction andconcentration gradients can vary along more than one axis of the pellet.The concentration gradient controls a reaction rate of the first andsecond reactants. Often the liquid delivery member delivers a greaterflow of liquid through the opening(s) closest to the liquid inlet side(the proximal end) as opposed to the flow of liquid through theopening(s) at the opposite distal end. As a result, it is generallydifficult across longer pellets to maintain equal liquid flow from oneend of the pellet to the opposite end of the pellet using a singleliquid delivery member that extends along the length of the pellet, dueto the variation in liquid flow rate and relatively long geometry. It isalso typical to experience non-uniform reaction and pelletdisintegration of the solid along the length of the pellet whichgenerally leads to loss of reaction surface area and earlier reductionin hydrogen flow. It would be advantageous to react the second reactantuniformly to maintain reaction surface area, maintain more consistentreaction product characteristics, and maintain a stable pellet assembly.For these reasons, the solid including the second reactant has aconcentration gradient that varies along an axis of the solid and theconcentration gradient controls the reaction rate of the first andsecond reactants. Where the liquid delivery member has first and secondends and a liquid flow output greater at the first end than the secondend, the concentration gradient is preferably lowest at the first endand higher at the second end. As a result, a more uniform reaction andpellet consumption is achieved.

In one embodiment, the solid has a composition that includes an acid andhas an acid concentration that varies along an axis such as length toprovide the concentration gradient. The presence of acid can acceleratethe reaction between the solid and liquid reactants, e.g., by dissolvingin and lowering the pH of the liquid. The concentration of the acid inthe solid may determine how quickly the first and second reactants reactto release hydrogen in the presence of the given amount of liquid. Byfirst characterizing the gradient of liquid flow rate, from the inletsection of the liquid delivery member to the opposite end of the liquiddelivery member at various hydrogen flow rate requirements, the acidconcentration from one end of the pellet to the other can be adjusted asa gradient to effectively account for the differing liquid reactant flowrates across the length of the liquid delivery member. Higher acidconcentrations could be used in portions of the solid where there isless liquid reactant flow, and less acid can be used in portions of thesolid where there is more liquid reactant flow. As a consequence,greater consumption of the solid pellet and its second reactant may bemaintained to ultimately achieve high hydrogen flow rates for longerperiods of time without having to tightly control liquid flow across theentire length of the solid surface. Similarly, the acid concentrationcan be adjusted to compensate for the presence of more unreacted liquidin the portion of the reaction area near where the effluent exits.

For a solid reactant such as sodium borohydride which has a higher rateof reaction at lower pH or in the presence of a catalyst, acid may be anadditive that reduces the pH of the reaction solution. The acid mayinclude a malic acid provided in different concentration levels withindifferent regions of the solid, according to one embodiment. Accordingto other embodiments, the acid may include one or more of citric acid,carbonic acid, malic acid, phosphoric acid, boric acid, succinic acid,sulfonic acid, and oxalic acid. The acid may vary in acidity from oneportion of the pellet to another portion. The change in acid throughouta path such as the length of the solid may be a continuous change or maybe distinct changes in different portions of the solid. According toanother embodiment, the type of acid employed in each portion of thepellet may be different to achieve different hydrogen release rateswithin each portion when the liquid first reactant is applied. It shouldfurther be appreciated that a base solution may be applied to one ormore regions of the solid to increase the pH and thus provide adiffering amount of acidity to different regions of the solid.

According to another embodiment, the concentration gradient provided inthe second reactant may be provided by employing different catalysts indifferent portions of the solid reactant. The catalyst may include oneor more transition metals from Group VIII such as iron, cobalt, nickel,ruthenium, rhodium, palladium, osmium, iridium and platinum, Group 1Bsuch as copper, silver and gold, and Group IIB such as zinc, cadmium,and mercury of the Periodic Table of the Elements, as well as othertransition metals including scandium, titanium, vanadium, chromium, andmanganese. Suitable catalysts also include metal salts, such aschlorides, oxides, nitrates, and acetates.

The type and/or amount of catalyst employed in each portion of the solidmay determine how quickly the solid reactant releases hydrogen in thepresence of a given amount of liquid reactant. The catalyst within eachsection extending along an axis such as a length of the solid can beadjusted to a gradient to effectively account for the differing liquidreactant flow rates across the length of the pellet and the delivery ofliquid reactant thereto. A higher concentration of catalyst may be usedwhere there is less liquid reactant flow and less catalyst can be usedwhere there is more liquid reactant flow. As a result, a greaterconsumption of the pellet and the solid reactant may be maintained toultimately achieve high hydrogen flow rates for longer periods of timewithout having to tightly control liquid flow across the entire lengthof the solid surface. The selection of different catalysts orconcentrations of one or more catalysts may be employed having differentcatalytic activities.

According to a further embodiment, the solid may include a hydrophilicmaterial that varies so as to provide the concentration gradient. Thehydrophilic material may include one or more of cotton, polyester,nylon, cellulose, carboxymethylcellulose, acrylic acids, and sodiumpolyacrylate. The hydrophilic material employed in each region of thesolid may vary based on the rate at which it absorbs or wicks water. Ahydrophilic material having a higher affinity for water could be usedwhere there is less liquid (e.g., water) flow and a lower affinity forwater used when there is more water flow. The type and/or amount ofhydrophilic material may be different in each region of the solid toachieve the concentration gradient. As a consequence, greaterconsumption of the pellets and the solid reactant may be maintained moreuniformly across the pellet.

According to yet another embodiment, the solid may include at least oneof density and porosity of the solid that varies to provide theconcentration gradient. The solid containing the second reactant mayhave a density or pososity that is greater in one portion compared tothe other portions. The density or porosity may vary continuously fromone portion to another or may include distinct changes in density orporosity extending from one end of the pellet to the opposite end. Thedensity or porosity of the solid may be higher in regions of the solidwhere there is higher liquid reactant flow as compared to regions of thesolid having less liquid reactant flow. Porous fibers such as polyvinylalcohol and rayon can be employed in the solid to achieve a desireddensity or porosity. As a consequence, greater and more uniformconsumption of the pellet and its solid reactant may be realized.

In yet another embodiment, the solid includes another constituent, suchas a binder, that varies to provide the concentration gradient. In thisembodiment and the embodiments described above, a concentration gradientof the solid reactant can also accompany the concentration gradient ofone or more other constituents of the solid.

Regardless of how the concentration gradient is produced, the change inconcentration can be continuous within the solid, incremental within thesolid from one portion (or individual pellet) to the next, or acombination of an incremental change from one portion to the next and acontinuous change within one or more portions.

In one embodiment, the solid reactant includes four distinct portionsincluding a first portion extending along a first length and having afirst reactant concentration, a second portion extending along a secondlength and having a second reactant concentration, a third portionextending along a third length and having a third reactantconcentration, and a fourth portion extending along a fourth length andhaving a fourth reactant concentration. The first, second, third andfourth reactant concentrations are of differing amounts so as to providethe concentration gradient from one end of the solid reactant extendingthe length to the opposite end. It should be appreciated that aplurality of differing solid reactant concentrations may be employed inany number of regions of two or more and that the variation inconcentration gradient may vary continuously or with distinct changes inportions of the pellet. The regions may extend in other directions suchas width or depth or other paths.

The generation of hydrogen gas can be controlled so hydrogen is producedas needed. Control can be based on one or more criteria, such as:pressure (e.g., internal pressure or a differential between an internaland an external pressure); temperature (e.g., hydrogen generator, fuelcell or device temperature); a fuel cell electrical condition (e.g.,voltage, current or power); or a device criterion (e.g., internalbattery condition, power input, or operating mode).

The hydrogen generator system can use a variety of reactants that canreact to produce hydrogen gas. Examples include chemical hydrides,alkali metal silicides, metal/silica gels, water, alcohols, dilute acidsand organic fuels (e.g., N-ethylcarbazole and perhydrofluorene). Atleast one reactant is included in the liquid stored in the reactantstorage area. The liquid can be a reactant or can contain a reactant(e.g., dissolved, dispersed or suspended therein).

As used herein, the term “chemical hydride” is broadly intended to beany hydride capable of reacting with a liquid to produce hydrogen.Examples of chemical hydrides that are suitable for use in the hydrogengenerator described herein include, but are not limited to, hydrides ofelements of Groups 1-4 (International Union of Pure and AppliedChemistry (IUPAC) designation) of the Periodic Table and mixturesthereof, such as alkaline or alkali metal hydrides, or mixtures thereof.Specific examples of chemical hydrides include lithium hydride, lithiumaluminum hydride, lithium borohydride, sodium hydride, sodiumborohydride, potassium hydride, potassium borohydride, magnesiumhydride, calcium hydride, and salts and/or derivatives thereof. In anembodiment, a chemical hydride such as sodium borohydride can react withwater to produce hydrogen gas and a byproduct such as a borate. This canbe in the presence of a catalyst, heat, a dilute acid or a combinationthereof.

Chemical hydrides can react with water to produce hydrogen gas andoxides, hydroxides and/or hydrates as byproducts. The hydrolysisreaction may require a catalyst or some other means of initiation, suchas a pH adjustment or heating. Chemical hydrides that are soluble inwater can be included in the liquid reactant composition, particularlyat alkaline pH to make the liquid sufficiently stable. The reaction canbe initiated by contacting the chemical hydride solution with acatalyst, lowering the pH (e.g., with an acid), and/or heating. Chemicalhydrides can be stored as a solid, and water can be added. A catalyst oracid can be included in the solid or liquid composition.

An alkali metal silicide is the product of mixing an alkali metal withsilicon in an inert atmosphere and heating the resulting mixture to atemperature of below about 475° C., wherein the alkali metal silicidecomposition does not react with dry O₂. Such alkali metal silicides aredescribed in U.S. Patent Application Publication No. 2006/0002839. Whileany alkali metal, including sodium, potassium, cesium and rubidium maybe used, it is preferred that the alkali metal used in the alkali metalsilicide composition be either sodium or potassium. Metal silicidesincluding a Group 2 metal (beryllium, magnesium, calcium, strontium,barium and radium) may also be suitable. In an embodiment, sodiumsilicide can react with water to produce hydrogen gas and sodiumsilicate, which is soluble in water.

A metal/silica gel includes a Group 1 metal/silica gel composition. Thecomposition has one or more Group 1 metals or alloys absorbed into thesilica gel pores. The Group 1 metals include sodium, potassium,rubidium, cesium and alloys of two or more Group 1 metals. The Group 1metal/silica gel composition does not react with dry O₂. Such Group 1metal/silica gel compositions are described in U.S. Pat. No. 7,410,567B2 and can react rapidly with water to produce hydrogen gas. A Group 2metal/silica gel composition, including one or more of the Group 2metals (beryllium, magnesium, calcium, strontium, barium and radium) mayalso be suitable.

One or more catalysts can be used to catalyze the hydrogen producingreactions. Examples of suitable catalysts include transition metals fromGroups 8 to 12 of the Periodic Table of the Elements, as well as othertransition metals including scandium, titanium, vanadium, chromium andmanganese. Metal salts, such as chlorides, oxides, nitrates and acetatescan also be suitable catalysts.

The rate of hydrogen generation can be controlled in a variety of ways,such as controlling of the rate at which liquid is transported to thereaction area, adjusting the pH, and making temperature adjustments. Therate of hydrogen generation can be controlled to match the need forhydrogen gas. A control system can be used for this purpose, and thecontrol system can be within or at least partially outside the hydrogengenerator.

Additives can be used for various purposes. For example, additives canbe included with a solid reactant as a binder to hold the solid materialin a desired shape or as a lubricant to facilitate the process offorming the desired shape. Other additives can be included in the liquidor the solid composition to control pH, to provide stability duringstorage and periods of nonuse, and to control the rate of reaction forexample. Such additives include but are not limited to acids (e.g.,citric, carbonic, malic, phosphoric and acetic acids or combinationsthereof), or basic compounds. Additives such as alcohols andpolyethylene glycol based compounds can be used to prevent freezing ofthe liquid. Additives such as surfactants or wetting agents can be usedto control the liquid surface tension and reaction product viscosity tofacilitate the flow of hydrogen gas and/or effluents. Additives such asporous fibers (e.g., polyvinyl alcohol and rayon) can help maintain theporosity of a solid reactant component and facilitate even distributionof the reactant containing liquid and/or the flow of hydrogen andeffluents.

In one embodiment, water is a first reactant and a chemical hydride suchas sodium borohydride (SBH) is a second reactant. The SBH can be storedas a solid in the reaction area. It can be present as a powder or formedinto a desired shape. If an increased rate of reaction between the SBHand the water is desired, a solid acid, such as malic acid, can be mixedwith the solid SBH, or acid can be added to the water. Solid (e.g.powdered) SBH can be formed into a solid mass, such as a block, tabletor pellet, to reduce the amount of unreacted SBH contained in theeffluent that exits the reaction area. The pellet should be shaped sothat it will provide a large contact surface area between the solid andliquid reactants.

In an example, a mixture including about 50 to 65 weight percent SBH,about 30 to 40 weight percent malic acid and about 1 to 5 weight percentpolyethylene glycol can be pressed into a pellet. Optionally, up toabout 3 weight percent surfactant (anti-foaming agent), up to about 3weight percent silica (anti-caking agent) and/or up to about 3 weightpercent powder processing rheology aids can be included in a pellet. Thedensity of the pellet can be adjusted, depending in part on the desiredvolume of hydrogen and the maximum rate at which hydrogen is to beproduced. A high density is desired to produce a large amount ofhydrogen from a given volume. On the other hand, if the pellet is tooporous, unreacted SBH can more easily break away and be flushed from thereaction area as part of the effluent. One or more pellets of this solidreactant composition can be used in the hydrogen generator, depending onthe desired volume of hydrogen to be produced by the hydrogen generator.The ratio of water to SBH in the hydrogen generator can be varied, basedin part on the desired amount of hydrogen and the desired rate ofhydrogen production. If the ratio is too low, the SBH utilization can betoo low, and if the ratio is too high, the amount of hydrogen producedcan be too low because there is insufficient volume available in thehydrogen generator for the amount of SBH that is needed. In anotherexample, a liquid including water is moved from the reactant storagearea to the reaction area to react with solid sodium borohydride (SBH).The liquid includes an acid such as malic acid to provide a low pH toproduce hydrogen gas at a desirable rate.

The hydrogen generator can include other components, such as controlsystem components for controlling the rate of hydrogen generation (e.g.,pressure and temperature monitoring components, valves, timers, etc.),safety components such as pressure relief vents, thermal managementcomponents, electronic components, and so on. Some components used inthe operation of the hydrogen generator can be located externally ratherthan being part of the hydrogen generator itself, making more spaceavailable within the hydrogen generator and reducing the cost byallowing the same components to be reused even though the hydrogengenerator is replaced.

The hydrogen generator can be disposable or refillable. For a refillablehydrogen generator, reactant filling ports can be included in thehousing, or fresh reactants can be loaded by opening the housing andreplacing containers of reactants. If an external pump is used to pumpfluid reactant composition from the reaction storage area to thereactant area, an external connection that functions as a fluid reactantcomposition outlet to the pump can also be used to refill the hydrogengenerator with fresh liquid reactant composition. Filling ports can alsobe advantageous when assembling a new hydrogen generator, whether it isdisposable or refillable. If the hydrogen generator is disposable, itcan be advantageous to dispose of components with life expectanciesgreater than that of the hydrogen generator externally, such as in thefuel cell system or an electrical appliance, especially when thosecomponents are expensive.

The reactant storage area, reaction area, and effluent storage area canbe arranged in many different ways, as long as effluent storage area isin a volume exchanging relationship with one or more of the reactantstorage and reaction areas that will allow the initially compressedfilter to expand as the effluent storage area increases in volume. Otherconsiderations in selecting an arrangement include thermal management(adequate heat for the desired reaction rate and dissipation of heatgenerated by the reactions), the desired locations of externalconnections (e.g., for hydrogen gas, liquid reactant flow to and from anexternal pump), any necessary electrical connections (e.g., for pressureand temperature monitoring and control of liquid flow rate), and ease ofassembly.

Referring to FIG. 1, a fuel cell system 10 is illustrated containing ahydrogen generator 14, according to one embodiment. Fuel cell system 10includes a fuel cell stack 12 and a removable hydrogen generator 14 forproviding hydrogen gas fuel to the fuel cell stack 12. The hydrogenpasses through an outlet valve 16 in the hydrogen generator 14, andthrough an inlet 24 to the fuel cell stack 12, where it is used as afuel by the anode. Another gas, such as oxygen, enters the fuel cellstack 12 through an inlet 26, where it is used as oxidant by thecathode. The fuel cell stack 12 produces electricity shown as voltageV_(O) that is provided to an electric device through a power output 28.Reactants within the hydrogen generator 14 react to produce thehydrogen. A liquid in the hydrogen generator 14 is transferred from areactant storage area to a reaction area where the hydrogen isgenerated. The liquid is transferred by a pump 22, which can be disposedwithin or outside the housing of hydrogen generator 14. If the pump 22is within the housing of the hydrogen generator 14, fewer externalconnections are needed, but if the pump 22 is an external pump, it cancontinue to be used after the used hydrogen generator 14 is replaced. Inthe embodiment shown, the pump 22 is shown outside the hydrogengenerator 14. The liquid can be pumped out of the hydrogen generator 14through an outlet valve 40 and back into the hydrogen generator 14through an inlet 20. The liquid can be a reactant-containing liquidreceived via liquid outlet passage 18 for producing hydrogen within thehydrogen generator 14. Outlet valve 40 may be controlled to select thequantity of reactant-containing liquid pumped into the hydrogengenerator 14 at a given time.

The fuel cell system 10 can include an optional control system forcontrolling the operation of the hydrogen generator 14 and/or the fuelcell stack 12. Components of the control system can be disposed in thehydrogen generator 14, the fuel cell stack 12, the apparatus powered bythe fuel cell system, or a combination thereof. The control system caninclude a controller 30. Although the controller 30 can be locatedwithin the fuel cell system 10 as shown, it can be located elsewhere inthe fuel cell system 10 or within the electric device for example. Thecontroller 30 can communicate through a communication line 32 with thepump 22, through a communication line 34 with the fuel cell stack 12,through a communication line 36 with the hydrogen generator 14 and valve40, and through a communication line 38 with the electric device.Sensors for monitoring voltage, current, temperature, pressure and otherparameters can be disposed in or in communication with those componentsso gas generation can be controlled based on those parameters.

The hydrogen generator 14 has a solid containing a second reactant has aconcentration gradient that varies along an axis of the solid and reactswith a first liquid reactant applied by a liquid delivery member asdescribed below with reference to FIGS. 2-4. The concentration gradientcontrols the reaction rate of the first and second reactants to achievea substantially uniform consumption of the reactant pellet and highliquid reactant flow rates for longer periods of time without having totightly control the liquid reactant flow across an entire path on thesurface of the solid reactant pellet. In the embodiment shown, the axisextends along the length of the solid. However, it should be appreciatedthat the axis may extend along other directions such as width or depthor other paths.

The hydrogen generator 14 includes a reactant storage area 58, areaction area 52 and an effluent storage area 74 within a housing 50.The liquid 60 is contained within the reactant storage area 58, and thesolid 54 is contained within the reaction area 52. The liquid 60includes a first reactant, such as a water and acid solution that can betransported to the reaction area 52. The solid 54 includes a secondreactant, such as a chemical hydride, and can be in the form of one ormore pellets. The effluent storage area 74 includes a filter, which canhave one or more filter components, such as three filter components 76,78 and 80. The reactant storage area 58 is enclosed by an enclosure 59such as a liquid impermeable bag.

The reaction area 52 can be at least partially enclosed by an enclosure56. The effluent storage area 74 can be enclosed by an optionalenclosure (not shown). Various types of enclosures can be used for thereactant storage area 58, the reaction area 52 and the effluent storagearea 74. For example, an enclosure can include internal surfaces of thehousing 50, other internal components of the hydrogen generator 14and/or it can share a common wall or section with one or more otherenclosures. All or portions of the enclosures can be flexible, rigid,stationary or moveable, preferably as long as the effluent storage area74 is in a volume exchanging relationship with at least one of thereactant storage area 58 and the reaction area 52. As shown, theenclosures 59 and 56 enclosing the reactant storage area 58 and thereaction area 52, respectively, are flexible enclosures that cancollapse as liquid 60 exits the reactant storage area 58, and effluentexits the reaction area 52. Examples of flexible enclosures includebags, balloons and bellows. It can be advantageous for flexibleenclosures to be elastic so they can be stretched when full and tend tocontract back to their original size as the contents exit, therebyhelping to expel fluids as the hydrogen generator 14 is operated.

During use of the hydrogen generator 14, liquid 60 is transported fromthe reactant storage area 58 to the reaction area 52 by any suitablemeans, as described above. For example, the liquid 60 can be transportedthrough a liquid outlet passage 18. If a pump is used, the pump 22 canbe within the housing 50, or it can be located externally as in theembodiment shown in FIG. 1. When a pump 22 is used, the liquid 60 can bepumped through the liquid outlet passage 18, such as a liquid outletconnection to the pump. Optional features, such as valves, filters andthe like can be incorporated into the liquid outlet connection 18. Anexternal pump 22 can pump the liquid 60 back into the hydrogen generator14 through a liquid inlet connection 20.

The hydrogen generator 14 includes a liquid delivery member 64 fortransporting and dispersing the liquid 60 to the solid 54 within thereaction area 52. The liquid delivery member 64 is connected to inlet 20such that the liquid 60 from the first reactant storage area 58 isdelivered to the reaction area 52. The liquid delivery member 64includes a first portion 72 and a second liquid distribution portion 75containing a plurality of openings 90 for delivering the liquid 60 tothe reaction area 52. The first portion 72 extends from the inlet 20 tothe liquid distribution portion 75. One or more openings 90 may beemployed to deliver the liquid 60 to the solid 54 to generate hydrogen.In the embodiment shown, the openings 90 are spaced throughout a lengthof the tubular liquid delivery portion 75 sufficient to deliver asufficient amount of liquid 60 over a sufficient area of the solid 54.

A portion of the reaction area 52 is shown in FIGS. 3 and 4 having thesolid 54 and the liquid delivery member 64 disposed on a top surfacethereof. The enclosure 56 (not shown) may include a polymeric bag orother liquid impermeable container that contains the solid 54 and itsreaction with the liquid 60 delivered thereto. An exhaust nozzle or port62 (not shown) may matingly engage the open end of the enclosure 56 andhave an opening for allowing hydrogen and effluent to exit the enclosure56. The liquid delivery member 64 may be integrally connected to theexhaust nozzle 62, according to one embodiment. This advantageouslyallows for the exhaust nozzle 62 to be assembled to the enclosure 56within a single opening, thereby minimizing the assembly thereof. Theliquid 60 can flow to the reaction area 52 through a liquid inletpassage, such as a tube connected to the inlet connection 20. Optionalfeatures such as valves, filters and the like can be incorporated intothe liquid inlet connection 20. The liquid 60 is delivered though theliquid delivery member 64 to disperse the liquid 60 over a large portionof the reaction area 52. The liquid delivery member 64 can include oneor more structures that extend into the reaction area 52. Thestructure(s) can be substantially linear, as shown in FIGS. 2-4, or theycan have other shapes.

The liquid delivery member 64 is shown in FIGS. 3 and 4 disposed on topof the solid 54 such that the liquid delivery member 64 contacts or isin close proximity to the solid 54. In FIG. 3, the solid 54 is shown notconsumed, and the liquid delivery member 64 lies on top of the solid 54and has a substantially straight arrangement that is not flexed. Asliquid 60 is transported through the liquid delivery member 64, theliquid exits openings 90 and is applied due to liquid flow and gravityand reacts with the second reactant in the solid 54 so as to consume thesolid 54 while generating hydrogen. As the second reactant is consumed,the solid 54 erodes such that its shape and size changes and becomessmaller. Hydrogen gas generated in the reaction area 52 exits throughthe exhaust nozzle and tends to carry with it reaction byproducts aswell as some of the unconsumed reactants. In addition, the flow ofliquid tends to be greater through the openings 90 at the inlet endrather than the outlet end of the liquid distribution portion 75,particularly when openings 90 have a uniform size. Both of these factorsresult in more of the liquid 60 on the side of the reaction area 52closest to the exhaust nozzle, such that the solid closest to theexhaust nozzle is consumed at a greater rate. While the plurality ofopenings 90 are shown evenly disposed throughout the liquid distributionportion 75 of the liquid delivery member 64, it should be appreciatedthat the openings 90 may be disposed unevenly throughout the liquiddistribution portion 75, according to other embodiments. The solid 54containing the second reactant is configured having a concentrationgradient that varies along an axis of the solid, such as along thelength of the solid, generally in a direction aligned with the liquiddelivery member. In the embodiment shown, solid 54 includes fourportions extending in four segments along the length of the solid 54,namely, first portion 54A, second portion 54B, third portion 54C andfourth portion 54D. Each of portions 54A-54D has a reactantconcentration that is different than the other of the portions 54A-54D.In one embodiment, the first portion 54A has a first reactantconcentration and the second portion 54B has a second reactantconcentration that is greater than the first reactant concentration. Thethird portion 54C has a third reactant concentration greater than thesecond reactant concentration. Similarly, the fourth portion 54D has afourth concentration greater than the third reaction concentration. Asliquid reactant flows into the inlet end toward the distal outer outletend of the liquid distribution portion 75, the liquid flow is less atthe outlet end as compared to the inlet end. By employing aconcentration gradient that has a lower reactant concentration in theportion 54A near the inlet end which increases towards the highestreactant concentration in the portion 54D near the liquid outlet end ofthe liquid distribution portion 75, a more uniform consumption of thesolid 54 may be achieved which may allow for enhanced flow rates forlonger periods of time. As a result, a more uniform consumption anddissipation of the solid 54 and its reactant may be achieved, as shownin FIG. 4. Each of the portions 54A-54D can be individual pellets, orthey can be portions of a unitary solid body 54, or the number ofportions in the solid body 54 can be varied as desired.

According to one embodiment, the solid employs an acid concentrationthat varies among different portions 54A-54D so as to achieve theconcentration gradient. In one embodiment, the acid concentration variesalong a longitudinal axis of the solid 54. As such, each of portions54A-54D has a different acidity. According to another embodiment, thetype of acid employed in each portion 54A-54D may be different such thateach portion achieves a different reaction rate to compensate for thevariation in liquid reactant flow exiting the liquid delivery member 64.The change in acid may be distinct change from one portion to another ormay include a continuous change within each region.

According to another embodiment, the solid employs different catalystsin different portions 54A-54D of the solid. This may include employing adifferent type and/or amount of catalyst within each of the regions54A-54D so as to provide the concentration gradient. A higherconcentration of catalyst may be used where there is less liquidreactant flow and less catalyst may be used where there is greaterliquid reactant flow. The catalyst may be selected to achieve a desiredreaction rate.

According to a further embodiment, the solid may employ a hydrophilicmaterial that varies in portions 54A-54D so as to provide theconcentration gradient. The hydrophilic material may include additivessuch as surfactants or wetting agents to control liquid surface tensionand reaction product viscosity to facilitate the flow of hydrogen gasand/or effluent or additives such as porous fiber. The selectedhydrophilic material may vary based on the rate at which it absorbs orwicks in the liquid. A hydrophilic material having a higher affinity forliquid (e.g., water) could be used where there is less liquid reactantflow and a lower affinity for water when there is more liquid reactantflow.

According to yet another embodiment, the solid may include at least oneof density and porosity of the solid that varies within each of regions54A-54D to provide the concentration gradient. The solid containing thesolid reactant may have a density that is greater in one portioncompared to the other portions. The density or porosity may varycontinuously within each portion or may be distinct changes between eachof the portions 54A-54D. The density or porosity of the solid may behigher in regions of the solid where there is higher liquid reactantflow as compared to regions of the solid having less liquid reactantflow.

It should be appreciated that the solid may be configured with otherconstituents that can be varied to provide a concentration gradientalong an axis of the solid, according to other embodiments.

When an internal or external pump 22 as shown in FIG. 1 is used, it canbe powered at least initially by an external power source, such as thefuel cell or another battery within a fuel cell system or an electricalappliance or device. If the pump 22 is within the container 50,connection can be made to an external power source through electricalcontacts. Alternatively, a battery can be located within the containerto at least start the pump 22.

The solid 54 contains a solid reactant that will react with the reactantcontained in the liquid in the reactant area 52. The solid 54 can be ina convenient form such as a pellet containing the second reactant andany desired additives. An optional catalyst can be included in ordownstream from the reaction area. For example, the catalyst can be onor part of the reaction area enclosure 56, dispersed in the solid 54, orcarried into the reaction area as part of the liquid 60.

Referring back to FIG. 2, as the liquid 60 comes in contact with thesolid 54, the first and second reactants react to produce hydrogen gasand byproducts. The hydrogen gas flows out of the reaction area 52 andthrough an effluent passage to an effluent entryway 86, where it entersthe effluent storage area 74. The hydrogen gas carries with it effluentthat includes byproducts as well as unreacted reactants and otherconstituents of the solid 54 and liquid 60. Where a reaction areaenclosure 56 is used, the effluent exits the reaction area 52 though anopening in the enclosure 56. The opening in the reaction area enclosure56 can include an exhaust nozzle 62, which can help keep the apertureopen. The exhaust nozzle 62 can optionally include a screen to holdlarge pieces of the solid 54 in the reaction area 52 to improveutilization of the second reactant. The effluent passageway can be astructure such as a tube (not shown) extending between the exhaustnozzle 62 and the effluent entryway 86, or it can be spaces that arepresent or develop between the exhaust nozzle 62 and the effluent entry86. Although it is desirable for the majority of the reactants to reactwithin the reaction area 52, unreacted reactants in the effluent cancontinue to react after exiting the reaction area 52. An optionalsecondary reaction area (not shown) can be included between the primaryreaction area 52 and the effluent storage area 74. Fresh liquid 60 canbe transported directly to this secondary reaction area, such as througha second fluid passage (not shown), to react with unreacted secondreactant in the effluent from the primary reaction area 52. A catalystcan be disposed within the secondary reaction area.

Hydrogen gas and effluent entering a proximal portion of the effluentstorage area 74 through the effluent entryway 86 flows through thefilter 76, 78 and 80 toward a distal portion of the effluent storagearea 74. As the hydrogen gas and effluent flow through the filter 76, 78and 80, hydrogen gas is separated from solid particles of the effluentby the filter 76, 78 and 80, which can be a single filter component ormultiple filter components, such as the three filter components 76, 78and 80. As described above, the filter 76, 78 and 80 can have portionsand/or filter components of different porosities, preferably increasingin porosity from the proximal portion toward the distal portion of theeffluent storage area 74, where the hydrogen gas exits the effluentstorage area 74.

The hydrogen gas may be separated from liquids and any remaining solidsin the effluent before exiting the hydrogen generator 14 by a hydrogenpermeable, liquid impermeable material. The hydrogen gas can exit thehydrogen generator 14 through a hydrogen outlet connection 16. Thehydrogen outlet connection 16 can be located near the distal portion ofthe effluent storage area 74 as shown in FIG. 2, or it can be locatedelsewhere, such as near the proximal portion of the effluent storagearea 74. If the hydrogen outlet connection 16 is not near the distalportion of the effluent storage area 74, the hydrogen gas can flow fromthe distal portion of the effluent storage area 74 to the hydrogenoutlet connection 16 through a hydrogen outlet passage 88, such as atube, which has a proximal end near the hydrogen outlet connection and adistal end 82 near the distal portion of the effluent storage area 74.The hydrogen gas can enter the hydrogen outlet passage 88 through thedistal end 82. The hydrogen permeable, liquid impermeable material canbe a component, such as a membrane, plug or filter element, preferablylocated at or near the distal end 82, or at least a portion of thehydrogen passage 88 can be made of a material that has high hydrogenpermeability and low or no liquid permeability. If only a portion of thehydrogen passage 88 is made from a material with high hydrogen, lowliquid permeability, that portion is preferably a distal portion tominimize the amount of solids in the effluent that comes in contact withand could clog the material, preventing hydrogen gas from exiting theeffluent storage area 74.

If the hydrogen outlet connection 16 is located near the distal portionof the effluent storage area 74, the hydrogen generator 14 can includean optional compartment positioned between the hydrogen outletconnection 16 and the hydrogen permeable, liquid impermeable material.Alternatively, at least a portion of an effluent storage area enclosure(e.g., a flexible bag) near the distal portion of the effluent storagearea 74 can be the hydrogen permeable and liquid impermeable material.

As shown, the effluent storage area 74 can be in a volume exchangingrelationship with both the reactant storage area 58 and the reactionarea 52. As the hydrogen generator 14 is used, reactant composition 60is transported from the first reactant storage area 58, which becomessmaller, to the reactant area 52, where first and second reactants areconsumed as they react to produce hydrogen and byproducts. The hydrogengas and effluents exit the reaction area 52, which becomes smaller, andenter the effluent storage area 74, which is able to become larger bygaining at least a portion of the quantity of volume lost by thereactant storage area 58 and the reaction area 52. As the effluentstorage area 74 becomes larger, the filter or at least one filtercomponent 76, 78 and 80 expands to partially or completely fill theenlarged volume and accommodate the hydrogen gas and effluent. Therelative sizes, shapes and locations of the areas 52, 58 and 74 can bevaried as described above, as can passageways, connections and the like,as long as the effluent storage area 74 is in a volume exchangingrelationship with at least one and preferably all of the reactantstorage area 58, and the reaction area 52, and the filter 76, 78 and 80is initially compressed and expands during operation of the hydrogengenerator as the volume of the effluent storage area 74 increases. Thelocations of other components, such as filter components, fluidconnections, passageways, dispersing members, nozzles and the like canalso be varied, whether the areas 52, 58, 74 are in the arrangementshown or in another arrangement.

The hydrogen generator 14 can include an optional moveable partition(not shown), between the effluent storage area 74 and adjacent portionsof the reactant storage area 58 and the reaction area 52, with themoveable partition able to move toward the reactant storage area 58 andthe reaction area 52 as those areas 52 and 58 become smaller and theeffluent storage area 74 becomes larger during operation of the hydrogengenerator 14, as long as there is an effluent entryway 86 through whicheffluent can pass into the effluent storage area 74. Such a moveablepartition can be used to facilitate compression of the filter componentsduring assembly of the hydrogen generator 14. The hydrogen generator 14can include other components not shown, as described above.

Referring to FIG. 5, a process of generating hydrogen gas with thehydrogen generator employing a concentration gradient in the solid isillustrated, according to one embodiment. Process 100 includes step 102of forming a solid including a solid reactant and having a concentrationgradient. The solid may be in the form of a single solid pellet having avarying concentration gradient or a plurality of solid pellets having aconcentration gradient. The concentration gradient may be realized witha variation in a reactant concentration according to one embodiment, anacid concentration and/or type according to another embodiment, acatalyst according to yet another embodiment, a hydrophilic materialaccording to a further embodiment, or a density and/or porosityaccording to yet a further embodiment. The solid reactant pellet(s) maybe formed of individual pellets defining separate regions that areassembled, bonded together or otherwise provided in contact or closeproximity. The concentration gradient may be distinct variations in thereactant concentration between regions, continuous within each region,or a combination thereof.

Process 100 further includes step 104 of delivering liquid reactant tothe solid. This may include delivering a liquid reactant by way of theliquid delivery member to a surface of the solid such that the liquidreactant reacts with the solid reactant. The concentration gradientcompensates for the rate of liquid reactant delivery so as to provide auniform consumption of the solid reactant, despite the potentialnon-uniform liquid flow. At step 106, process 100 generates hydrogen gasat a reaction rate that is determined by the concentration gradient. Theconcentration gradient affects the reaction rate within a given regionand is configured to provide more uniform consumption of the solidreactant. At step 108 process 100 outputs the hydrogen gas which may beuseful for a fuel cell or other hydrogen consuming device.

A variety of materials are suitable for use in a hydrogen generator,including those disclosed above. Materials selected should be resistantto attack by other components with which they may come in contact (suchas reactant compositions, catalysts, effluent materials and hydrogengas) as well as materials from the external environment. The materialsand their important properties should also be stable over the expectedtemperature ranges during storage and use, and over the expectedlifetime of the hydrogen generator.

Suitable materials for the housing and internal partitions can includemetals, plastics, composites and others. Preferably the material is arigid material that is able to tolerate expected internal pressures,such as a polycarbonate or a metal such as stainless steel or anodizedaluminum. The housing can be a multi-component housing that is closedand sealed to securely hold the components of the hydrogen generator andprevent hydrogen gas from leaking therefrom. Various methods of closingand sealing can be used, including fasteners such as screws, rivets,etc., adhesives, hot melts, ultrasonic bonding, and combinationsthereof.

Suitable materials for flexible enclosures can include polypropylene,polyethylene, polyethylene terephthalate and laminates with a layer ofmetal such as aluminum. If an elastic enclosure is desired, suitablematerials include silicone and rubbers.

Suitable materials for tubing, etc., used to transport fluid reactantcomposition and effluents can include silicone, TYGON® andpolytetrafluoroethylene.

Suitable materials for filters and filter components can include foammaterials. A foam material can have an open cell structure (an open cellfoam) or closed cell structure (a closed cell foam). Generally a majorpart of the foam filter will have an open cell structure. In someembodiments the filter component or a portion thereof can have a closedcell structure or a skin on one or more surfaces, depending on thedesired porosity and permeability to solids, liquids and gases. Thefilter components can be made from elastomeric foams, preferable with aquick recovery (low compression set/high recovery). The elastomer may bea resilient cured, cross-linked or vulcanized elastomer, for example.Examples of suitable elastomeric materials include one or more of: apolyurethane elastomer, a polyethylene, a polychloroprene (neoprene), apolybutadiene, a chloroisobutylene isoprene, a chlorosulphonatedpolyethylene, an epichlorohydrin, an ethylene propylene, an ethylenepropylene diene monomer, an ethylene vinyl acetate, a hydrogenatednitrile butadiene, a polyisoprene, an isoprene, an isoprene butylene, abutadiene acrylonitrile, a styrene butadiene, a fluoroelastomer, asilicone, and derivatives and combinations thereof.

Other materials that can be used for the filter components includereticulated materials such as reticulated polyesters (e.g., polyethyleneterephthalate), polyethylene, polyurethane, polyimide, melamine, nylon,fiberglass, polyester wool and acrylic yarn. As disclosed above, thefilter does not necessarily have to be made of a material that canexpand by itself after being compressed if another means of expandingthe filter is provided.

Suitable materials for a liquid delivery or dispersing member caninclude a liquid impermeable material, such as tubular or other hollowcomponents made from materials such as silicone rubber, TYGON® andpolytetrafluoroethylene, polyvinylidene fluoride (PVDF) and fluorinatedethylene-propylene (FEP), with holes or slits formed therein; a liquidpermeable member made from a material such as cotton, a nylon, anacrylic, a polyester, ePTFE, or a fritted glass that can allow the fluidreactant composition to pass through or that can wick the liquidreactant composition; or a combination, such as a hollow liquidimpermeable material with holes or slits therein and wrapped in,surrounded by or coated with a material that can wick the liquidreactant composition.

All references cited herein are expressly incorporated herein byreference in their entireties. To the extent publications and patents orpatent applications incorporated by reference contradict the disclosurecontained in the present specification, the present specification isintended to supersede and/or take precedence over any such contradictorymaterial.

It will be understood by those who practice the invention and thoseskilled in the art that various modifications and improvements may bemade to the invention without departing from the spirit of the disclosedconcept. The scope of protection afforded is to be determined by theclaims and by the breadth of interpretation allowed by law.

The invention claimed is:
 1. A solid including a solid reactant for usein a hydrogen generator, said solid having a longest dimension along anaxis of the solid and comprising: a first portion extending along afirst segment of the longest dimension of the solid and having a firstsolid reactant concentration uniform throughout the first portion; and asecond portion extending along a second segment of the longest dimensionof the solid and having a second solid reactant concentration uniformthroughout the second portion and different than the first solidreactant concentration, wherein the first and second solid reactantconcentrations provide a concentration gradient along the axis of thelongest dimension of the solid.
 2. The solid of claim 1, wherein thesolid comprises an acid, wherein an acid concentration in the first andsecond portions varies to provide the concentration gradient.
 3. Thesolid of claim 1, wherein the solid comprises a catalyst, wherein thecatalyst in the first and second portions varies to provide theconcentration gradient.
 4. The solid of claim 1, wherein the solidcomprises a hydrophilic material that varies in the first and secondportions to provide the concentration gradient.
 5. The solid of claim 1,wherein the solid has at least one of density or porosity that varies inthe first and second portions to provide the concentration gradient. 6.The solid of claim 1 further comprising a third portion extending alonga third segment of the longest dimension and having a third solidreactant concentration uniform throughout the third portion, wherein thethird solid reactant concentration is different than the first andsecond solid reactant concentrations.
 7. The solid of claim 6 furthercomprising a fourth portion extending along a fourth segment of thelongest dimension and having a fourth solid reactant concentrationuniform throughout the fourth portion, wherein the fourth solid reactantconcentration is different from the first, second and third solidreactant concentrations.
 8. The solid of claim 4, wherein thehydrophilic material comprises one or more of cotton, polyester, nylon,cellulose, carboxymethylcellulose, acrylic acids, and sodiumpolyacrylate.
 9. The solid of claim 1, wherein the solid is a solid bodycomprising one or more pellets.
 10. The solid of claim 1, wherein thesolid reactant comprises sodium borohydride.
 11. The solid of claim 4,wherein the hydrophilic material comprises one or more surfactants andwetting agents.